To obtain a natural color image as seen by the human eye, an imaging device using a solid-state imaging element such as a CMOS image sensor (CIS) essentially requires an optical article which shields light in the near-infrared range of 800 to 1,000 nm detected by a sensor, transmits light in the range of 400 to 600 nm, and thus can approximate human visibility.
As such an optical article, a reflective near-infrared shielding filter including a dielectric multilayer film or an absorbing near-infrared shielding filter using a fluorophosphate-based glass containing a divalent copper ion as a coloring component may be used.
However, a conventionally used reflective near-infrared shielding filter has a limit in that it cannot be applied to a high-resolution camera module with 5 or more mega pixels since a phenomenon of taking an unintended image (hereinafter, referred to as “ghosting” or “ghost image”) when an image is taken by an imaging device due to internal reflection between an optical filter and a lens of a solid-state imaging element, particularly, between an optical filter and a CIS microlens.
In addition, a conventional absorbing near-infrared shielding filter has a preferable effect of shielding light in the wavelength range from 800 to 1,000 nm, but due to low durability because of the properties of a material, it is difficult to be manufactured thin and thus is easily breakable.
Therefore, there is an urgent demand for development of an optical article which can shield light in the wavelength range from 800 to 1,000 nm, and can be manufactured to be thinner.